Question

I get a crazy error and I am unable to see why it happens.
I have made a simple app that uses a TabBar to navigate 3 views. I created everything and added one UIImageView to each of the 3 ViewControllers that the TabBar manages. Everything works fine. In the app you are able to navigate the 3 views and see the 3 images.

Now I add one UIButton (or any other component) to the 1st ViewController. I add it in the NIB and in my code I do the usual:

IBOutlet UIButton *btn;
@property (nonatomic, retain) IBOutlet UIButton *btn;

@synthesize btn;
[btn release];

and connect the UIButton in my NIB to the “btn”. Now the app crashes as soon as the TabBar tries to show this view (which is imediately after it launches) giving me a:

2009-08-24 16:52:25.164
AppName[2249:207] *** Terminating app
due to uncaught exception
‘NSUnknownKeyException’, reason:
‘[
setValue:forUndefinedKey:]: this class
is not key value coding-compliant for
the key btn.’

I tried restarting the SDK, my computer, building for 2.2.1, 3.0, for simulator, for device, cleaning all targets, etc but the problem remains. I am sure it has something to do with the UITabBarController. I just can’t see what.

Answer 1

I had a similar problem. It was because the UIViewController for the tab was not set to the specific subclass of UIViewController I had created.

If you look at the .xib in IB you’ll see something like this:

  **Name**                **Type**
  File's Owner        UIApplication
  First Responder     UIResponder
  Tab Bar Controller  UITabBarController
     Tab Bar          UITabBar
     View Controller  UIViewController
     View Controller  UIViewController
     View Controller  UIViewController

The View Controllers under the tab bar controller will default to a basic UIViewController. You need to change their class to your subclassed view controller in order for them to load and connect to your outlets correctly:

  **Name**                **Type**
  File's Owner        UIApplication
  First Responder     UIResponder
  Tab Bar Controller  UITabBarController
     Tab Bar          UITabBar
     FirstTab View Controller  MyFirstTabController
     SecondTab View Controller MySecondTabController
     ThirdTab View Controller  MyThirdTabController

Then when the tab creates the controller for your tab it will be creating the correct class. Note, this is probably why your viewDidLoad method is not called